<select name="cbxModelo"required>	
	<option value=""><?= STR_VALOR_INICIAL?></option>
	<?php foreach ($modelo as $m):?>
	<option value="<?= $m->id_modelo?>" <?php if(isset($edit)){ if($edit[0]->id_modelo == $m->id_modelo){ echo 'selected'; } }?>>
		<?= $m->nombre ?>
	</option>
	<?php endforeach; ?>
</select>